(a) Field of the Invention
The present invention relates to a welding gun device, more particularly, a projection welding gun device that applies pressure to a protrusion portion that is formed in a welding portion of a metal member and applies current through the protrusion portion to concentrate resistance heat therein.
(b) Description of the Related Art
In general, during a manufacturing process of a vehicle, various structural parts such as a vehicle body panel molded by a press and the like are bonded by a method such as welding to complete an integrated vehicle body, the completed vehicle body is painted and rust-prevented throughout the surface of each part in a painting process and thereafter, a design process is performed, such as assembling a power train system. Further, parts such as suspension, steering, and braking systems are assembled and subsequently, a door, a trunk lid, a hood, and the like are assembled.
Further, in a vehicle body assembling process of the vehicle, spot resistance welding through a spot welding apparatus is frequently used as a method for bonding two vehicle body panels in bonding vehicle body parts such as a roof, a pillar, a side panel, an opening unit flange of a vehicle body door, and the like.
Spot resistance welding in which pressing force is applied to a vehicle body panel surface, which is deposited by electrical resistance, is generally achieved through a spot welding apparatus installed at an arm front end of a robot for spot welding.
However, the spot welding device forms a press mark, and there is a drawback that the press mark deteriorates external appearance quality.
Particularly, after the painting process, the press mark that is formed by a welding process is not eliminated, is exposed, and may result in deteriorated product quality.
To address this drawback, a laser brazing welding is used or a cover is used to hide the welding portion, but such methods may increase manufacturing costs.
Recently, a protrusion has been formed on a lower panel so as to address the drawback of spot welding, and an electrical resistance welding is provided in which the protrusion is pressed and the current is applied through the protrusion, which is known as projection welding.
Projection welding typically involves applying high current and low pressing force to the panel such that the press mark is not formed on the panel.
Projection welding is a resistance welding that uses a projection welding gun having an upper welding tip and a lower welding tip that are mounted through a shank, where the upper welding tip presses an upper panel corresponding to a protrusion portion after forming the protrusion portion on a lower panel.
In this case, a rectangle type and a circular type may be used for a projection welding gun device.
However, in the projection welding gun device, when the rectangle type welding tip is mounted, a welding gun is to be disposed in a vertical direction on the protrusion, but the welding gun is not disposed in the vertical direction due to the interference with a jig for fixing the panel on the production site.
In this configuration, because the welding tip does not completely cover the protrusion, there is a drawback that a protruded portion is formed after the welding process.
Also, when a circular welding tip is mounted thereon, because an angle of the protrusion and the welding gun become flexible, the welding can be performed without the interference with the jig.
However, in a case that a curved surface is formed on the panel, the welding tip forms a line contact with the panel, and there is a drawback that line mark is formed on the panel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.